oncoming aeroplane. And it was coming on
rapidly, showing that it had tremendous power, for it was a very large
one, carrying three men.

"How do you suppose they got on our track?" asked Ned.

"Oh, we must have been reported from time to time, as we flew over
cities or towns," replied Mr. Petrofsky. "You know we're rather large,
and can be seen from a good distance. Then too, the whole Russian
secret police force is at the service of our enemies."

"But we're not over Russia yet," said Mr. Damon.

Ivan Petrofsky took the telescope and peered down toward the earth.
They were not a great way above it, and at that moment they were
passing a small village.

"Can you tell where we are?" asked the odd man.

"We are just over the border of the land of the Czar," was the quiet
answer. "The imperial flag is flying from a staff in front of one of
the buildings down there. We are over Russia."

"And here comes that airship," called Ned suddenly.

They gazed back with alarm, and saw that it was indeed so. The big
aeroplane had come on wonderfully fast in the last few minutes.

"Tom! Tom!" cried his chum. "Better get ready to make a sprint."

"I'm all ready," calmly answered our hero. "Shall I go now?"

"If you can give us a few seconds longer I may be able to tell who is
after us," remarked Mr. Petrofsky, turning his telescope on the craft
behind them.

"I can let them get almost up to us, and get away," replied Tom.

The Russian did not answer. He was gazing earnestly at the approaching
aeroplane. A moment later he took the glass down from his eye.

"It's our spy again," he said. "There are two others with him. That is
one of the aeroplanes owned by the secret police. They are stationed
all over Europe, ready for instant service, and they're on our trail."

The pursuing craft was so near that the occupants could easily be made
out with the naked eye, but it needed the glass to distinguish their
features, and Mr. Petrofsky had done this.

"Shall I speed up?" cried Tom.

"Yes, get away as fast as you can!" shouted the Russian. "No telling
what they may do," and then, with a hum and a roar the motor of the
Falcon increased its speed, and the big airship shot ahead.

CHAPTER XVI

THE NIHILISTS

From the pursuing aircraft came a series of sharp explosions that
fairly rattled through the clear air.

"Look out for bombs!" yelled Ned.

"Bless my safety match!" cried Mr. Damon. "Are they anarchists?"